JPH06283699A - Original reader - Google Patents

Abstract

PURPOSE:To read an inverted after-image generated in an original reader generally called 'a contact type image sensor' and to read an image at a faster speed. CONSTITUTION:An original reader 10 has a photodiode 14, a blocking diode 16 and channel wirings C1, C2,..., Cn, and comprises lower electrodes 14a, 16a of the photodiode 14 and the diode 16 having a multilayer structure of metal layers 14a1, 16a1 made of chromium and n-type semiconductor layers 14a2, 16a2 made of ITO, etc. Thus, a barrier is formed in on the interface between the layers 14b, 16b and the layers 14a2, 16a2 to prevent a reverse current flowing immediately after it its switched from a reading state to a storage stage, thereby improving a switching speed of the diode 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device, and more particularly, to a document reading device used in an image reading section for inputting image information in a facsimile, an image scanner or the like.

[0002]

2. Description of the Related Art In recent years, a document reading device generally called a contact image sensor has been widely adopted in an image reading section of a facsimile or the like, instead of a CCD type document reading device which requires a reduction optical system.

For example, as shown in FIG. 5, a conventional document reading apparatus 1 includes a glass substrate 2, a photodiode 3 which is a photoelectric conversion element, a blocking diode 4 which is a switching element, and an electric signal from the photodiode 3. Channel wiring C _1, C _{2, ...} C _n for reading out
And are formed.

The photodiode 3 and the blocking diode 4 are both opaque lower electrodes 3a and 4a made of metal and a pin made of amorphous silicon.
Structured semiconductor layers 3b and 4b and ITO (Indium Tin Oxi
de) and transparent upper electrodes 3c and 4c are sequentially deposited. The photodiode 3 and the blocking diode 4 are covered with a transparent interlayer insulating film 5 made of SiO _x, and are connected in series in reverse polarity by a connecting wire 7 through a contact hole 6 formed in the interlayer insulating film 5. Has been done. On the other hand, the lower electrode 3a forming the photodiode 3 has the channel wirings C _1, C via the contact hole 8 formed in the interlayer insulating film 5.
_{2, ...} C _n . Further, these are entirely covered with the protective film 9.

The photodiode 3 and the blocking diode 4 are arranged in a one-dimensional array as shown in FIG.
× n blocks are arranged, and m blocks B _{1 and} B are arranged for every n blocks.
_{2, ...} have been divided into B _m, anode electrode blocks B _1, B 2 blocking diode _{4, ...} are connected in common in a B _m, the anode electrode of the photo diode 3 channel wiring C _{1 ,} C _{2, ...} C _n by blocks B _1, B
_{2, 2, ...,} B _m , which are relatively in the same position, are commonly connected.

This document reading device 1 operates by a charge storage system, and as shown in the time chart of FIG.
Drive pulse _{Vp 1, Vp 2, ... Vp} m blocks B _1, B _{2, ...} B
Each block B _1, B is applied with a cycle T in sequence for every _{m.
2, ...} B _m repeats the read state at time t and the storage state at time T−t. From the blocks B _1, B _{2, ...} B _{m in the} read state, output currents Iout _1, Iout _{2, ...} Iout _n corresponding to the amount of light incident during the storage state up to that point.
Flow out through the channel wirings C _1, C _{2, ...} C _n , and these output currents Iout _1, Iout _{2, ...} Iout _n are amplified and integrated by an external signal processing circuit, and then in time series. Will be output. For example, when the first block B ₁ is in the read state, the output currents Iout _{1 and} Iout from the first block B _{1 are} output.
_{2, ...} Iout _n flows out, then the first block B ₁ is in the accumulation state and the second block B ₂ is in the reading state,
Output current from the second block B ₂ Iout _1, Iout _{2, ...} Iout _n
Will flow out.

[0007]

[Problems to be Solved by the Invention] However, in reality,
Immediately after the blocks B _1, B _{2, ...} B _m are switched from the read state to the storage state, the output currents Iout _1, Iout _{2, ...} Iout _n
Current in the opposite direction (hereinafter referred to as "reverse current") Ir _1, Ir
_{2, ...} Ir _n flows. This reverse current Ir _1, Ir _{2, ...} Ir _n
The normal output current is Iout _1, Iout _{2, ...} Iout _n 1
It reaches 0 to 20%, and its convergence time Tr reaches the order of 10 ⁻³ seconds. Therefore, for example, the first block B ₁
When white is read by the second block B ₂ and black is read by the third block B ₃ , output currents Iout _1, Iout flowing when the second block B ₂ is in the read state
_{2, ...} Iout _n becomes smaller than usual, and the output currents Iout _1, Iout _{2, ...} Iout _n that should not flow when the third block B ₃ is in the read state are the reverse currents Ir _{1 ,} Ir
_{2, ...} Ir _n will flow in the opposite direction. However, as in the case of the third block B ₃ in this case, immediately after the blocks B _1, B _{2, ...} B _{m in} which black is read are switched from the read state to the accumulated state, the reverse current Ir _{1 ,} Ir _{2, ...} Ir
_n does not flow.

In such a phenomenon, in the reproduced image, the black read immediately after the white is read is blacker than the normal black,
White that is read immediately after reading black appears whiter than normal white, and is therefore called “reversal afterimage”. In particular, white is read by the first block B _1, if the ash (brightness 10-20% white) is read in the second block B _2, the output current from the second block B ₂ Iout _{1 ,} Iout
_An accurate signal output was not obtained, such as _{2, ...} Iout _n showed black. Also, in order to reduce power consumption, etc., there is a tendency to read a document under low illuminance, but even under low illuminance, the size of the reversal afterimage does not decrease, only the size of the signal output decreases, so the reversal afterimage However, there was a problem that the relative proportion of To avoid as much as possible this state, the drive pulse Vp _1, Vp _2, ... it is necessary to take a longer width t of Vp _m, there is a problem that the signal reading speed becomes slow.

Therefore, the present inventors have conducted intensive studies in order to reduce the afterimage of inversion and enable faster reading, and as a result, the present invention has been achieved.

[0010]

An object of a document reading apparatus according to the present invention is to provide an optical sensor element comprising a photoelectric conversion element and a switching element connected in series with the photoelectric conversion element on a substrate. Are arranged in one dimension,
Those which are divided into a plurality of blocks by a certain number, and one of these photosensor elements is commonly connected in the block, and the other is relatively located at the same position between the blocks by channel wiring. And the photoelectric conversion element comprises a lower electrode, a semiconductor layer deposited on the lower electrode, and a transparent upper electrode deposited on the semiconductor layer, and the switching element is a lower electrode. In a document reading device comprising an electrode, a semiconductor layer deposited on the lower electrode, and an upper electrode deposited on the semiconductor layer, at least the lower electrode constituting the switching element has one or more metal layers. And an n-type semiconductor layer deposited on the metal layer.

In such a document reading apparatus, the n
The type semiconductor layer consists of ITO.

Further, in such a document reading apparatus,
The metal layer consists of chromium.

Further, in such a document reading apparatus, at least the upper electrode forming the photoelectric conversion element is made of ITO.

Further, in such a document reading apparatus,
The photoelectric conversion element and the switching element each have diode characteristics and are connected in series with opposite polarities.

Further, in such a document reading apparatus, the respective semiconductor layers forming the photoelectric conversion element and the switching element are made of amorphous silicon continuously deposited by plasma CVD method, and pi
It has an n structure.

Further, in such a document reading apparatus,
The lower electrode, the semiconductor layer, and the upper electrode, which form the photoelectric conversion element and the switching element, are simultaneously deposited.

[0017]

According to such a document reading apparatus, the lower electrode constituting the switching element is composed of the metal layer made of chromium or the like and the n-type semiconductor layer made of ITO or the like, and the semiconductor layer and the n-type semiconductor layer. The interface with is formed. At this interface, a potential barrier and a barrier such as a trap level generated by diffusing a substance forming the n-type semiconductor layer into the semiconductor layer are formed, and most of the reverse current is blocked by this barrier. it is conceivable that. As a result, the reverse current is rapidly converged, the peak value thereof is reduced, and the switching speed of the switching element is improved. As a result, the afterimage of inversion is reduced and the signal reading speed is increased.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the document reading apparatus according to the present invention will be described in detail with reference to the drawings.

As shown in FIGS. 1 and 2, a document reading apparatus 10 according to the present invention includes a photodiode 14 as a photoelectric conversion element and a switching element on an optically transparent substrate 12 made of glass or the like. A certain blocking diode 16 and channel wirings C _1, C _{2, ...} C _n for reading an electric signal from the photodiode 14 are formed and configured. Here, the photodiode 14 and the blocking diode 16 form an optical sensor element.

The photodiode 14 and the blocking diode 16 are both the lower electrode 1 having a two-layer structure.
4a, 16a and p made of amorphous silicon or the like
In-structured semiconductor layers 14b and 16b and ITO (Indium
Transparent upper electrodes 14c, 16 composed of tin oxide)
and c are sequentially deposited. These lower electrodes 14a and 16a are composed of metal layers 14a ₁ and 16a ₁ made of Cr, Ni, Pd, Ti, Mo, Ta, Al, etc., ITO, SnO ₂ ,
It is composed of n-type semiconductor layers 14a ₂ and 16a ₂ made of TiO ₂ or amorphous silicon.

The photodiode 14 and the blocking diode 16 are covered with a transparent interlayer insulating film 18 made of SiO _x , SiN _x or the like, and connection wiring is formed through a contact hole 20 formed in the interlayer insulating film 18. 22 are connected in series with opposite polarities. That is, the photodiode 14 and the blocking diode 16 are connected by the cathode electrodes. On the other hand, the lower electrode 14a of the photodiode 14 is the interlayer insulating film 18
Are connected to the channel wirings C _1, C _{2, ...} C _n through the contact holes 24 formed in the. Further, these are entirely covered with the protective film 26.

Further, as in the conventional case, the photodiode 14 and the blocking diode 16 are one-dimensionally m ×.
There are n blocks, and m blocks B _1, B _{2, ...}
Have been classified into B _m, anode electrode blocks B _1, B 2 blocking diodes _{16, ...} they are connected in common in a B _m, anode electrode channel wiring C ₁ of the photodiode _14, C _{2,. .. by} C _n blocks B _1, B
_{2, 2, ...,} B _m , which are relatively in the same position, are commonly connected.

Here, an example of a method of manufacturing the document reading apparatus 10 will be briefly described.

First, a metal film of Cr, Ni, Pd, Ti, Mo, Ta, Al or the like is deposited on the substrate 12 by a vacuum vapor deposition method using an electron beam or resistance heating, or a sputtering method using DC or RF. Then, an n-type semiconductor film such as ITO, SnO ₂ or amorphous silicon is deposited on this by a vacuum deposition method, a sputtering method or the like.
Further thereon, a p-type amorphous silicon film in which holes serve as majority carriers is formed by a plasma CVD method or the like,
An i-type amorphous silicon film that serves as an intrinsic semiconductor and an n-type amorphous silicon film that serves as majority carriers of electrons are successively deposited. Then, a transparent conductive film such as ITO or SnO ₂ is deposited again on this by a vacuum evaporation method, a sputtering method, or the like. The film thickness of the metal film and the n-type semiconductor film is preferably several hundred to several thousand liters, and is appropriately determined in consideration of the characteristics of these films and the performance of the amorphous silicon film.

Next, the upper transparent conductive film, the three-layer amorphous silicon film, and the lower n-type semiconductor film are patterned into a predetermined shape by a photolithography method or the like, and then the metal film is changed into another predetermined shape. Then, the photodiode 14 and the blocking diode 16 are formed by patterning.

Next, on the photodiode 14 and the blocking diode 16, a thermal CVD method and atmospheric pressure C are applied.
VD method, a plasma CVD method, after depositing the like SiO _x and SiN _x by a sputtering method to form the interlayer insulating film 18 by patterning into a predetermined shape by a photolithography method so. At this time, the photodiode 14, the blocking diode 16, and the contact hole 20, at a predetermined position on the metal layer 14a ₁ .
While forming 24, the interlayer insulating film 18 is removed in the region on the metal layer 16a ₁ where the extraction electrode 28 is formed.

Further, a metal such as Cr, Ni, Pd, Ti, Mo, Ta, and Al is deposited in a single layer or a multi-layer on them by a vacuum vapor deposition method, a sputtering method or the like, which is then photolithographically By patterning into a predetermined shape, the connection wiring 22 and the channel wirings C _1, C
_{2, ...} C _n and the extraction electrode 28 are formed. This allows
The upper electrodes 14c, 16c are electrically connected to each other by the connection wiring 22, and the metal layer 14a ₁ and the channel wirings C _1, C
_{2, ...} C _n are electrically connected. In addition,
These materials are not particularly limited as long as they can be electrically connected and are not particularly limited.

Finally, the plasma CVD method,
After depositing silicon oxide, silicon nitride, tantalum oxide, or the like by a sputtering method or the like, patterning the silicon oxide, silicon nitride, or tantalum oxide into a predetermined shape by a photolithography method, the extraction electrode 28 and the channel wirings C _1, C _{2, ...
A} protective film 26 is formed so as to cover the entire region except the _n extraction electrode (not shown). The protective film 26 is for protecting the photodiode 14, the blocking diode 16, the channel wirings C _1, C _{2, ...} C _n from humidity and scratches.

Here, the metal film and the n-type semiconductor film are deposited in a blanket state, and then the amorphous silicon film is deposited. However, before depositing this amorphous silicon film, only the n-type semiconductor film is deposited first. The n-type semiconductor layers 14a ₂ and 16a ₂ may be formed by patterning. In this case, the upper electrodes 14c and 16c and the semiconductor layer 14b,
16b and then, the blanket-state metal film is patterned to form the metal layers 14a ₁ and 16a ₁ .
It has the same configuration as the above-mentioned document reading apparatus 10. The deposition of the metal layer and the n-type semiconductor layer may be continuously performed without breaking the vacuum, or may be discontinuously performed once the vacuum is broken. Further, although the method of patterning mainly by the photolithography method is illustrated here, it may be formed by a mask method or the like so that the film is not deposited on unnecessary portions from the beginning, and the manufacturing method is not limited at all. Not something.

In this document reading apparatus 10, since the lower electrodes 14a and 16a are composed of the metal layers 14a ₁ and 16a ₁ and the n-type semiconductor layers 14a ₂ and 16a ₂ , the semiconductor layers 14b and 16b and the n-type semiconductors are formed. Layers 14a ₂ and 16a
_Two interfaces are formed. It is considered that a potential barrier or a barrier such as a trap level generated by diffusing the substance forming the n-type semiconductor layers 14a ₂ and 16a ₂ into the semiconductor layers 14b and 16b is formed at this interface. Therefore, the reverse currents Ir _1, Ir _{2, ...} Ir flowing immediately after the blocks B _1, B _{2, ...} B _m are switched from the read state to the storage state _.
Most of _n is considered to be blocked by this barrier, and the reverse currents Ir _1, Ir _{2, ...} Ir _n are converged in the order of 10 ⁻⁵ to 10 ⁻⁶ seconds, and their peak values are also set. Get smaller. As a result, the switching speed of the blocking diode 16 is improved and the inversion afterimage is significantly reduced. Therefore, of course, accurate signal output can be obtained.
It is also possible to increase the signal reading speed. Furthermore, since the afterimage of reversal is sufficiently reduced, accurate signal output can be ensured even when a document is read under low illuminance, and power consumption can be reduced.

Next, in order to confirm the effect of the document reading apparatus according to the present invention, a comparative experiment was conducted using the example and a comparative example using a conventional document reading apparatus. This will be described below.

EXAMPLE A substrate 12 was made of Corning non-alkali glass (# 7).
059), a chromium film having a thickness of 1500 to 2000 Å is first deposited on the substrate 12 by a DC sputtering method, and an ITO film having a thickness of 1200 Å which is an n-type semiconductor film is further deposited.
The film was deposited. Specifically, the substrate 12 is set in a chamber, the chamber is evacuated to 10 ⁻⁵ Torr or less, and then the substrate 12 is held at 100 to 250 ° C. under a pressure of 0.1 to 1.0 Pa and DC. Electric power 0.1-1.0W / c
A chromium film and an ITO film were sequentially deposited by introducing argon gas and oxygen gas at a constant ratio under m ² . Furthermore, on this, by the plasma CVD method,
50-300Å thick p-type amorphous silicon film, 7
An i-type amorphous silicon film having a thickness of 000 to 12000Å and an n-type amorphous silicon film having a thickness of 50 to 300Å were sequentially deposited. And again on this, IT mentioned above
A 600 Å thick ITO film was deposited in the same manner as the O film.

Then, by photolithography,
The upper ITO film, the amorphous silicon film composed of three layers, and the lower ITO film which is an n-type semiconductor film are patterned into a predetermined shape to form upper electrodes 14c and 16c, semiconductor layers 14b and 16b, The n-type semiconductor layers 14a ₂ and 16a ₂ which are part of the lower electrodes 14a and 16a were formed. Specifically, a resist solution was applied on the upper ITO film, prebaked, and then exposed using a mask in which a predetermined pattern was engraved. After development and post-baking, the upper ITO film was etched with a mixed solution of hydrochloric acid and nitric acid. Next, the amorphous silicon film was etched using a parallel plate type etching device. Here, after the chamber was evacuated to 10 ^-3 Torr or less, CF ₄ gas and O ₂ gas were introduced, and while maintaining the pressure at 5.0 Pa, a high frequency power supply of 13.56 MHz was used to apply 0.1 to the electrode. The amorphous silicon film was etched by supplying electric power of 0.7 W / cm ² . Then, again, the lower ITO film which is the n-type semiconductor film was etched with a mixed solution of hydrochloric acid and nitric acid.

Then, after removing the resist used for patterning, the chromium film was patterned into a predetermined shape by photolithography to form metal layers 14a ₁ and 16a ₁ which are a part of the lower electrodes 14a and 16a. Cerium ammonium nitrate was used for etching the chromium film.

The photodiodes 14 and the blocking diodes 16 were formed in this manner. The number of these photodiodes was 1728, and the number of these photodiodes was 32 for every 32.
It was divided into blocks. Further, as shown in FIG. 2, the size of the photodiode 14 is 105 μm × 125 μm, and the size of the blocking diode 16 is 33 μm ×
It was 33 μm.

Next, a silicon oxide film having a thickness of 1.5 μm was deposited on the photodiode 14 and the blocking diode 16 by the plasma CVD method. That is, after evacuating the inside of the chamber to 10 ^-2 Torr or less, the substrate 12 is heated and maintained at a predetermined temperature, and silane gas 20
Introduce sccm and nitrous oxide gas 150-300 sccm,
The pressure was maintained at 0.3 to 1.2 Torr (here, nitrogen gas may be introduced if necessary). After that, after waiting for the pressure to stabilize, a high frequency power source of 13.56 MHz is used to apply 0.01 to 0.5 to the electrode facing the substrate 12.
A silicon oxide film was deposited by supplying electric power of W / cm ² . Next, the interlayer insulating film 18 was formed by patterning into a predetermined shape by photolithography. A parallel plate type etching apparatus was used for the etching here.

Further, two layers of Cr and Al are deposited on these by a sputtering method and patterned into a predetermined shape by a photolithography method, and the connection wiring 22 and the channel wirings C _1, C _{2, ...} C _{n are formed.} And the extraction electrode 28 were formed. Here, the film thickness of Cr was 500 Å and the film thickness of Al was 1.5 μm. Al etching was performed with a mixed solution of phosphoric acid, hydrochloric acid, nitric acid and acetic acid, and Cr etching was performed with ceric ammonium nitrate.

Finally, a 5000 Å thick silicon nitride film was deposited on the entire surface by the plasma CVD method. That is, after exhausting the inside of the chamber to 10 ^-2 Torr or less,
The substrate 12 is heated and maintained at a predetermined temperature, and silane gas 20 to 6 is used.
0 sccm and 150 to 300 sccm of ammonia gas were introduced and the pressure was maintained at 0.3 to 1.2 Torr (here, hydrogen gas or nitrogen gas may be introduced if necessary). Then wait for the pressure to stabilize and wait 13.5
A silicon nitride film was deposited by supplying a power of 0.01 to 0.5 W / cm ² to the electrode facing the substrate 12 using a high frequency power source of 6 MHz. Next, the protective film 26 was formed by patterning into a predetermined shape by photolithography. A parallel plate type etching apparatus was also used for the etching here.

Next, a driving circuit and a signal processing circuit were connected to these Examples and Comparative Examples, and the frequency of the clock pulse was set to 500 KHz and the reading speed was set to 5 msec / line. It was illuminated with the illuminance of Lux and read. As a result, from the signal processing circuit, as shown in FIG.
The output voltage Vout shown in FIG. In the figure, the output voltage Vout of the embodiment is shown by a solid line.

Comparative Example On the other hand, as a comparative example of the conventional document reading apparatus, FIG.
As shown in, the lower electrodes 3a and 4a were made up of only the metal layer and no transparent conductive layer was produced. The lower electrodes 3a and 4a were formed by depositing a chromium film having a thickness of 1500 to 2000 Å by a sputtering method and patterning the chromium film by a photolithography method.

Then, in the same manner as in the example, the driving circuit and the signal processing circuit were connected to the obtained document reading device to read the document changing from white to black. As a result, the output voltage Vout shown in FIG. 3 was obtained from the signal processing circuit. In this figure, the output voltage Vout of the comparative example is shown by the dotted line.

As described above, the inverted afterimage Vr appears in the output voltage Vout immediately after reading white, which causes black read immediately after reading white to be blacker than normal black. However, the inversion afterimage Vr of the example was smaller than the inversion afterimage Vr of the comparative example, and the convergence time was also shorter. Table 1 shows a summary of the results. Here, the output voltage Vout corresponding to white is 160 to 180 mV
Met.

[Table 1]

Although one embodiment of the document reading apparatus according to the present invention has been described in detail above, the present invention is not limited to the above-mentioned embodiment and can be implemented in other modes.

For example, in the above-described embodiment, the upper electrode 14c forming the photodiode 14 and the upper electrode 16c forming the blocking diode 16 are connected by the connection wiring 22, but as shown in FIG. A lower electrode 30 that constitutes the diode 14 and a lower electrode 30 that constitutes the blocking diode 16 are common, and the original reading device 32 in which the photodiode 14 and the blocking diode 16 are connected by this lower electrode 30. Good. In this case, the metal layer 34 and the n-type semiconductor layer 36 are sequentially deposited to form the lower electrode 3
0, and the semiconductor layers 14b and 16b and the n-type semiconductor layer 3
The interface with 6 may be formed. Further, the upper electrode 14c of the photodiode 14 is taken out by a lead wiring 38 and connected to the channel wirings C _1, C _{2, ...} C _n, and the upper electrode 16c of the blocking diode 16 is taken out by a lead wiring 40. Good. In this example, the photodiode 14 and the blocking diode 16 are connected to each other at their anode electrodes, and are connected in series with opposite polarities.

Further, in the above-mentioned embodiment, the metal layer 14
a ₁ , 16a ₁ , 34 and n-type semiconductor layers 14a ₂ , 16a
_{Although 2} and 36 have different shapes, they may have the same shape.

Further, in the above-mentioned embodiment, the anode electrode or the cathode electrode of the blocking diode 16 is commonly connected in the blocks B _1, B _{2, ...} B _m , and the anode electrode or the cathode electrode of the photodiode 14 is the channel. Blocks B _1, B _{2, ...} B by wires C _1, C _{2, ...} C _n
Although they are connected to each other at the same position between _m , the photodiode and the blocking diode are reversed, and the anode electrode or the cathode electrode of the photodiode is connected in common in the block, and the blocking diode is connected. The anode electrode or the cathode electrode may be connected to each other at a relatively same position between the blocks by channel wiring. That is, a plurality of optical sensor elements each including a photodiode (photoelectric conversion element) and a blocking diode (switching element) are one-dimensionally arrayed and divided into a plurality of blocks for every predetermined number. It suffices that one of them is commonly connected within the block, and the other is commonly connected by those located at the same relative position between the blocks by the channel wiring.

Further, in the above-mentioned embodiment, the lower electrodes 1 constituting the photodiode 14 and the blocking diode 16 are constituted for the reason of simplifying the manufacturing process.
4a, 16a, semiconductor layers 14b, 16b and upper electrode 1
4c and 16c are deposited at the same time and are made of the same material. The upper electrode 14c of the photodiode 14 must be transparent, but the upper electrode 16c of the blocking diode 16 is It does not have to be transparent. Further, the lower electrode 14a forming the photodiode 14 does not have to be formed of a metal layer and an n-type semiconductor layer, and at least the lower electrode 16a forming the blocking diode (switching element) 16 has a metal layer 16a _1. And n-type semiconductor layer 1
6a ₂ and the like. That is, in the present invention, the interface between the semiconductor layer forming the switching element and the n-type semiconductor layer may be formed to prevent the reverse current generated in the switching element. The metal layer may be one layer, but may be two or more layers.

Although the semiconductor layers 14b and 16b described above are both stacked in the order of pin from the substrate 12 side, conversely, they may be stacked in the order of nip to have a pin structure. In addition to the pin type described above, n
The i-type, pi-type, pn-type, MIS-type, heterojunction-type, homojunction-type, Schottky barrier-type, or a combination thereof may be deposited in a single layer or multiple layers. Furthermore, as the amorphous silicon constituting the semiconductor layer, hydrogenated amorphous silicon a-Si: H, hydrogenated amorphous silicon carbide a-SiC: H, amorphous silicon nitride, etc., and simple amorphous silicon a-Si etc. are preferable. However, these structures are not limited at all, for example, an amorphous silicon-based semiconductor made of an alloy of silicon and another element such as carbon, germanium, tin, or the like may be deposited.

Besides, the photoelectric conversion element may be, for example, a photoconductive element instead of a photovoltaic element such as a photodiode. Further, the present invention can be carried out in a mode in which various improvements, corrections, and modifications are made based on the knowledge of those skilled in the art, such as a TFT may be used as the switching element, without departing from the spirit of the invention.

[0050]

According to the document reading apparatus of the present invention, at least the lower electrode forming the switching element is composed of one or more metal layers and an n-type semiconductor layer deposited on the metal layers, Since the interface between the layer and the n-type semiconductor layer is formed, the reverse current is rapidly converged by the barrier formed at this interface, and its peak value is also reduced, so that the switching speed of the switching element is improved. To be made. Therefore, the afterimage of inversion is reduced and an accurate signal output can be obtained. In particular, it is advantageous when reading a document under low illuminance, and power consumption can be reduced. Further, the present invention has various excellent effects such as the fact that the signal reading speed can be significantly increased.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a document reading apparatus according to the present invention.

FIG. 2 is a partial plan view of the document reading apparatus shown in FIG.

FIG. 3 is a graph showing an output voltage of an actually manufactured document reading apparatus, showing a result of a comparative experiment conducted for confirming the effect of the present invention.

FIG. 4 is a schematic sectional view showing another embodiment of the document reading apparatus according to the present invention.

FIG. 5 is a schematic sectional view showing an example of a conventional document reading apparatus.

FIG. 6 is a circuit diagram of the document reading apparatus shown in FIG.

FIG. 7 is a time chart for explaining the operation of the document reading apparatus shown in FIGS. 5 and 6.

[Explanation of symbols]

10, 32; original reading apparatus 12; the substrate 14; a photodiode (photoelectric conversion element) 16; blocking diode (switching elements) 14a, 16a, 30; the lower electrode 14a _1, 16a _1, 34; metal layer 14a _2, 16a ₂ , 36; n-type semiconductor layers 14b and 16b; semiconductor layers 14c and 16c; upper electrode

Claims (7)

[Claims] 1. A plurality of optical sensor elements, each of which is composed of a photoelectric conversion element and a switching element connected in series with the photoelectric conversion element, are one-dimensionally arranged on a substrate, and are divided into a plurality of blocks for every predetermined number. In addition, one of these photosensor elements is commonly connected within the block, and the other is commonly connected between those at relatively the same position between the blocks by the channel wiring. The conversion element includes a lower electrode, a semiconductor layer deposited on the lower electrode, and a transparent upper electrode deposited on the semiconductor layer, and the switching element is a lower electrode and deposited on the lower electrode. In a document reading device including a semiconductor layer and an upper electrode deposited on the semiconductor layer, at least one lower electrode that constitutes the switching element is one or more layers. And the metal layer, the document reading apparatus characterized by being composed of an n-type semiconductor layer deposited on the metal layer. 2. The document reading device according to claim 1, wherein the n-type semiconductor layer is made of ITO. 3. The document reading apparatus according to claim 1, wherein the metal layer is made of chromium. 4. The document reading device according to claim 1, wherein at least an upper electrode forming the photoelectric conversion element is made of ITO. 5. The document reading according to claim 1, wherein the photoelectric conversion element and the switching element each have a diode characteristic and are connected in series with opposite polarities. apparatus. 6. Each of the semiconductor layers forming the photoelectric conversion element and the switching element is made of amorphous silicon continuously deposited by a plasma CVD method,
The original reading device according to any one of claims 1 to 5, which has a pin structure. 7. The lower electrode, the semiconductor layer, and the upper electrode forming the photoelectric conversion element and the switching element are deposited at the same time, respectively. A document reading device according to claim 2.